1. Field of the Invention
The present invention relates to a motor having a frequency generator comprising a frequency generating base plate on which a frequency generating coil pattern and a land are formed and a multipole magnetized magnet arranged at the position which faces the frequency generating base plate, in which when these base plate and magnet relatively move, a signal of a frequency proportional to the rotational speed of a rotary driving apparatus which is generated from the frequency generating coil pattern is output from the land to another base plate.
2. Related Background Art
As the prior arts regarding the motor having a frequency generator, the following prior arts are known.
(1) U.S. Pat. No. 4,260,920 (Japanese Patent Application No. 111646/1977) PA0 (2) U.S. Pat. No. 3,796,899 PA0 (3) Official Gazette of Japanese Patent Examined Publication No. 35,027/1983 PA0 (4) Official Gazette of Japanese Patent Unexamined Publication No. 91,111/1977 PA0 (5) Official Gazette of Japanese Patent Examined Publication No. 20,267/1984 PA0 (6) And the like
FIG. 1 and 2 show a constitution disclosed in U.S. Pat. No. 4,260,920. Namely a rotary shaft 2 is inserted into a bearing 16 mounted at the center of a disk-shaped yoke plate 15 and rotatably supported thereby. The yoke plate 15 made of magnetic material and it is spaced from the lower side of a magnet 4 when the rotary shaft 2 is inserted into the bearing 16, to define a magnetic air gap 17 between the yoke plate 15 and the magnet 4. Disposed within the air gap 17 are first and second star-shaped driving coils 18 and 19, each of which is manufactured by winding a copper wire approximately sixty turns in the shape of a square and bending centers of four sides of the square inwardly to form a star-shape. The driving coils 18 and 19 are angularly displaced from each other by an electrical angle of 90.degree. or a mechanical angle of 22.5.degree.. Disposed on an upper side of the yoke plate 15 are washers 20, 21, and 22, on which an insulative base plate 23 made of synthetic resin is mounted. The base plate 23 and the washers 20, 21, and 22 are fixed to the yoke plate 15 by bolts 25 which extend from an upper side of the base plate 23 to the lower side of the yoke plate 15. The driving coils 18 and 19 are bonded to a lower side of the base plate 23. Disposed on the upper side of the base plate 23 is a velocity detecting coil 24 which has a plurality of generating element wires 26 27 28, . . . 29 each connected in series to others with an inner end of one wire being connected to an outer end of the adjacent wire to form a pair of output terminals 30 and 31. Each of the generating element wires 26, 27, 28, . . . 29 extends inward from the outer periphery of the magnet 4 and has a length substantially equal to a radial length of each of the velocity detecting magnetic poles of the magnet 4. The velocity detecting coil 24 is formed by printing it on the upper side of the base plate 23.
Disposed on the upper side of the yoke plate 15 are a pair of Hall effect elements 32 and 33 which are mounted on an insulative board 34 and arranged around the center of the rotary shaft 2 to be angularly displaced from each other by an electrical angle of 90.degree. or a mechanical angle of 22.5.degree. and to interlink with magnetic fluxes of the driving magnetic poles 6, 7, 8, . . . 9. The insulative board 34 is bonded to the yoke plate 15.
In such a constitution, a FG (frequency generating) signal which is generated when the motor rotates is, in general, waveform shaped and thereafter, it is supplied to a servo circuit and used to control the rotational speed of the motor. Therefore, a variation in period of the signal which is derived by waveform shaping the FG signal results in a noise in the speed control system and causes the whole system to be adversely influenced by this noise.
The output terminals 30 and 31 of tee frequency generating element wires 26, 27, . . . 29 set forth in U.S. Pat. No. 4,260,920 are located in the outside of the generating element wires 26, 27, . . . 29. Therefore, lead-out wire portions of the output terminals 30 and 31 are influenced by the leakage magnetic fluxes of the magnet 4, so that the frequency generating output signal (FG output) having the designed value cannot be obtained. For example, as the frequency generating output signal, assuming that a signal A shown by a solid line in FIG. 3A has a normal waveform, a period P.sub.1 of the waveform after waveform shaping the signal A which is derived from the lead-out wires which are not influenced by the leakage magnetic fluxes from the magnet 4 is always constant as shown in FIG. 3B.
However, as shown in FIG. 1, when the lead-out wires are disposed outward from the frequency generating element wires 26, 27, . . . 29, the signal is influenced by the leakage magnetic fluxes from the magnet 4 and the output waveform changes as shown by a signal B indicated by alternate long and two short dashes line in FIG. 3A. Namely, the voltage signal across the lead-out wires is increased or decreased in accordance with the positions of the magnetic poles N and S of the magnet 4. Thus, the period after the signal was waveform shaped becomes a period P.sub.2 larger than a predetermined reference value P.sub.1 or a period P.sub.3 smaller than P.sub.1 as shown in FIG. 3C. When the period of the FG output from the frequency generator is larger than the reference value P.sub.1, the servo circuit of the motor determines (detects) that the rotational speed of the motor is smaller than a predetermined rotational speed on the basis of the frequency of the period P.sub.2 and increases a current or voltage to a motor driving circuit, thereby allowing the motor to rotate at an acceleration speed.
On the contrary, in the case of the period P.sub.3 smaller than the reference value P.sub.1, the servo circuit determines that the motor rotational speed is larger than the reference speed and outputs a deceleration control signal. Therefore, the motor repetitively irregularly rotates at an acceleration speed and a deceleration speed.
Further, in the motor having the frequency generator, as well as the influence on the signal lead-out wires by the leakage fluxes, there is another factor which exerts an adverse influence on the output signal of the frequency generator. Namely, the lead wires or the like which are connected from the signal output end portions (land portions) of the frequency generating coils to the motor servo circuit are influenced by the leakage magnetic fluxes from the magnet. Therefore, if the lead wires are disposed so as to cross the leakage magnetic fluxes of the magnet, a current flows through the lead wires, so that the problem as previously mentioned with respect to FIGS. 3A, 3B, and 3C occurs.